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Highlights (1) Evaluation of deformation superposition behavior of asphalt mixture by the multi-point penetration test. (2) Determinant of the deformation superposition resistance of the asphalt mixture under the multi-wheel load is wheel spacing and the number of wheels. (3) The reduction of tensile chains is the internal reason for asphalt mixture deformation superposition. (4) The numerical simulation method can reflect the laboratory penetration test outcome.

Abstract Relevant mechanical parameters of asphalt composites, such as the dynamic modulus and phase angle, are obtained by means of four-point bending tests. It is a dynamic test based on the application of sinusoidal load pulses and sinusoidal displacement response. A sinusoidal response can be difficult to record due to different issues, such as noise during an experiment. In strain-controlled tests with the application of a low-load amplitude with asphalt mixtures at high temperatures composed with calcined clay, which is the case of the test carried out in this study, a relationship was observed between the apparent noise recorded and the frequencies of the beam’s natural vibration. This outcome led to the conclusion that these imperfections are not a result of failures in the procedure, but of the natural behavior of the beam. This conclusion can assist in the filtering of information to obtain better results.

Warm Mix Asphalt (WMA) refers to a variety of asphalt mixtures produced at lower temperatures than those conventionally used to produce hot mixture asphalt. These reductions in the production temperatures provide social, economic, and environmental gains. This study aimed to investigate the mechanical properties of asphalt mixtures composed of asphalt binders modified with sunflower oil at the addition contents of 1%, 2%, and 3%. Indirect tensile strength, resilient modulus, water sensitivity, dynamic modulus, rutting resistance, and fatigue life of the asphalt mixtures were evaluated. Results showed that the mechanical performance of asphalt mixtures composed of oil-modified asphalt binder decreased compared to that of the mixture with neat asphalt binder, even though all of them are suitable for application in surface courses according to the current technical requirements for asphalt concretes. However, asphalt mixtures with sunflower oil-modified binders presented enhances in adhesion, which indicates less susceptibility to moisture than their equivalent non-modified.

This study aimed to address the issue of high-temperature challenges in asphalt pavement by developing two types of phase change materials (PCMs) for temperature control. Encapsulated paraffin wax particles (EPWP) and encapsulated myristic acid particles (EMAP) were synthesized using acid-etched ceramsite (AECS) as the carrier, paraffin wax (PW) or myristic acid (MA) as the core material, and a combination of epoxy resin and cement as the encapsulation material. The investigation encompassed leakage tests on PCMs; rutting plate rolling forming tests; SEM, FTIR, XRD, and TG-DSC microscopic tests; as well as heat storage and release tests and temperature control assessments using a light heating device. The study revealed the following key findings. Both types of PCMs exhibited no PCM leakage even under high temperatures and demonstrated low crushing ratios during rut-forming tests. Microscopic evaluations confirmed the chemical stability and phase compatibility of the constituents within the two types of PCMs. Notably, the phase change enthalpies of EPWP and EMAP were relatively high, measuring 133.31 J/g and 138.52 J/g, respectively. The utilization of AECS as the carrier for PCMs led to a substantial 4.61-fold increase in the adsorption rate. Moreover, the PCMs showcased minimal mass loss at 180 °C, rendering them suitable for asphalt pavement applications. The heat storage and release experiments further underscored the PCMs’ capacity to regulate ambient temperatures through heat absorption and release. When subjected to light heating, the maximum temperatures of the two types of phase change Marshall specimens were notably lower by 6.6 °C and 4.8 °C, respectively, compared to standard Marshall specimens. Based on comprehensive testing, EPWP displayed enhanced adaptability and demonstrated substantial potential for practical implementation in asphalt pavements.

The present paper presents the rutting evaluation of different asphalt mixtures in use in the state of Rio Grande do Sul, Brazil's southernmost-region, through the uniaxial repeated load test and the monitoring of mixtures performance in field, culminating in a criteria proposal for the parameter Flow Number depending on traffic. For this, five distinct asphalt binders were studied, five grain size distributions, three warm mixtures and 21 hot mixes, with different mineralogical types of aggregates, and 15 monitored test sites distributed geographically throughout the state. The results indicated that the binder modifications were the most influential characteristics in the asphalt mixtures rutting. Also, it was verified that the Flow Number criteria proposed so far in the country present significant differences. In this way, a new criterion was suggested, and it is possible to infer a good applicability for asphalt concretes, except for warm mixes and those with rubber binder. [ABSTRACT FROM AUTHOR]

This review paper shows several sections of bitumen, asphalt mixtures, polymers, and waste plastic in pavement engineering. The paper reviews and evaluates the influence of using waste polymer in improving the rheological and engineering properties of the modified binder and mixtures. Evaluation of properties and design of stone mastic asphalt mixtures are reviewed. Reports and studies had investigated the advantages and importance of using polymer in bitumen modification; however, they yet show a gap in research in terms of the role of waste polymer in improving the durability, aging, and fatigue life in the long term of service. [ABSTRACT FROM AUTHOR]

Variations in pavement density have been widely monitored and investigated, both in laboratory and in field experiments, since the compaction of pavement is so critical to its long-term performance quality. In contrast to field testing, laboratory tests are simpler to produce but less accurate. Destructive drilled samples are used to conduct field testing; however, they are limited in their ability to assess density information at specific areas. The use of computationally aided approaches, such as the Finite Element Method (FEM) and the Discrete Element Method (DEM), in research involving asphalt mixtures is increasing, since these methods simulate and evaluate the characteristics of asphalt mixtures at macroscopic and microscopic scales. Individual particle behavior at the microscopic level cannot be fully represented using the FEM alone, and the computing cost of utilizing the DEM approach alone is prohibitively high. The objective of this work is to simulate the pre-compaction process by using the coupled FEM-DEM approach. In order to investigate the impact of the asphalt mixtures' gradation, a dense-graded asphalt mixture (AC 11) and a gap graded asphalt mixture (PA 11) were simulated. Different paving speeds (4, 5, and 6 m/min) were applied on the preliminary compaction model of AC 11 to study the effect of the paving speeds on the compaction process. By comparing the angular velocity, which worked as a reference of compaction quality, it was demonstrated that the grade AC 11 asphalt mixtures performed better in the preliminary compaction process compared to the grade PA 11 asphalt mixtures. Moreover, since it has an effect on compaction, paving speed was carefully monitored and kept within a reasonable range in order to maximize both pavement quality and project efficiency. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the permanent deformation of unmodified and styrene-butadiene-rubber (SBR) modified asphalt mixtures using dynamic creep test. The purpose was to assess the effect of SBR as one of the most plentiful and low-cost polymers in Iran on rutting resistance of asphalt mixtures in the regions with hot climate, such as the areas around the “Persian Gulf”, and the central deserts of the “Iran Plateau”. First, the critical gradation of aggregates with higher permanent deformation was determined. Then, the aggregates with critical gradation were mixed with the optimum amount of bitumen modified by different amounts of SBR, and tested to obtain an optimum SBR content with lower permanent deformation. Finally, the unmodified and SBR-modified asphalt mixtures with optimum SBR content (6%wt) were tested at 40 and 50 ˚C as the simulated ambient temperatures in order to evaluate the effect of SBR and rising temperature on rutting resistance of the asphalt mixtures. In addition, the flow number (FN) of asphalt mixtures is calculated according to Goh and You method. Results showed that with addition of 6% SBR, the permanent strains of asphalt mixtures decreased by 39 and 60%, and the creep modulus increased by 64 and 133% at 40 and 50 ˚C, respectively. Furthermore, with the temperature rising from 40 to 50 ˚C, the permanent strains of asphalt mixtures containing 0 and 6% SBR increased by 61 and 5%, and their creep modulus decreased by 34 and 6%, respectively. The FNs of unmodified samples were obtained 8416 and 9728 loading cycles at 40 and 50 ˚C, respectively. In contrast, up to the last loading cycle, the SBR-modified samples did not experience the tertiary flow at both ambient temperatures. These results let us conclude that the SBR-modified bitumen is able to significantly reduce the permanent deformations, and enhance the resilience and creep modulus of asphalt mixtures; moreover, it can minimize the negative effects of rising temperature on their engineering properties.

Asphalt aging is one of the main factors causing asphalt pavements deterioration. Previous studies reported on some aging benefits of asphalt rubber mixtures through laboratory evaluation. A field observation of various pavement sections of crumb rubber modified asphalt friction courses (ARFC) in the Phoenix, Arizona area indicated an interesting pattern of transverse/reflective cracking. These ARFC courses were placed several years ago on existing jointed plain concrete pavements for highway noise mitigation. Over the years, the shoulders had very noticeable and extensive cracking over the joints; however, the driving lanes of the pavement showed less cracking formation in severity and extent. The issue with this phenomenon is that widely adopted theories that stem from continuum mechanics of materials and layered mechanics of pavement systems cannot directly explain this phenomenon. One hypothesis could be that traffic loads continually manipulate the pavement over time, which causes some maltenes (oils and resins) compounds absorbed in the crumb rubber particles to migrate out leading to rejuvenation of the mastic in the asphalt mixture. To investigate the validity of such a hypothesis, an experimental laboratory testing was undertaken to condition samples with and without dynamic loads at high temperatures. This was followed by creep compliance and indirect tensile strength testing. The results showed the higher creep for samples aged with dynamic loading compared to those aged without loading. Higher creep compliance was attributed to higher flexibility of samples due to the rejuvenation of the maltenes. This was also supported by the higher fracture energy results obtained for samples conditioned with dynamic loading from indirect tensile strength testing.

This study explores the potential in substituting ordinary Portland cement (OPC) with industrial waste silica fume (SF) as a mineral filler in asphalt mixtures (AM) for flexible road pavements. The Marshall and indirect tensile strength tests were used to evaluate the mechanical resistance and durability of the AMs for different SF and OPC ratios. To develop predictive models of the key mechanical and volumetric parameters, the experimental data were analyzed using artificial neural networks (ANN) with three different activation functions and leave-one-out cross-validation as a resampling method. The addition of SF resulted in a performance comparable to, or slightly better than, OPC-based mixtures, with a maximum indirect tensile strength of 1044.45 kPa at 5% bitumen content. The ANN modeling was highly successful, partly due to an interpolation-based data augmentation strategy, with a correlation coefficient RCV of 0.9988.

Self-healing in asphalt mixtures is a property that can be enhanced by external heating, which causes a thermal expansion that increases the flow of bitumen with reduced viscosity through the cracks. Therefore, this study aims to evaluate the effects of microwave heating on the self-healing performance of three asphalt mixtures: (1) conventional, (2) with steel wool fibers (SWF), and (3) with steel slag aggregates (SSA) and SWF. After evaluating the microwave heating capacity of the three asphalt mixtures with a thermographic camera, their self-healing performance was determined with fracture or fatigue tests and microwave heating recovery cycles. The results demonstrated that the mixtures with SSA and SWF promoted higher heating temperatures and presented the best self-healing capacity during the semicircular bending test and heating cycles, with significant strength recovery after a total fracture. In contrast, the mixtures without SSA presented inferior fracture results. Both the conventional mixture and that containing SSA and SWF presented high healing indexes after the four-point bending fatigue test and heating cycles, with a fatigue life recovery of around 150% after applying two healing cycles. Therefore, the conclusion is that SSA greatly influences the self-healing performance of asphalt mixtures after microwave radiation heating.

The demand for more sustainable transport infrastructure has led to a broader acceptance of waste materials in pavements. An excellent example of this trend is the incorporation of steel slag aggregates (SSA) in asphalt mixtures. This work evaluates the mechanical performance of asphalt mixtures that include SSA in their composition. Asphalt mixtures were evaluated through laboratory tests for affinity between binder and aggregate, Marshall and volumetric properties, stiffness, resistance to fatigue, permanent deformation, and water sensitivity. Two rates of SSA incorporation—20% and 35%—were considered. In general, results indicated that incorporating SSA has not impaired the behavior of the asphalt mixtures. In some cases, the presence of SSA has improved mechanical performance. It was the case of the resistance to permanent deformation, stability, flow, and water sensitivity. This work confirms the suitability of the SSA application in asphalt mixtures beyond the benefit of promoting industrial waste in pavement engineering.

A novel approach utilizing in-situ Computed Tomography (CT) scanning and digital image processing techniques was developed to overcome the limitations of traditional CT image analysis in studying microcrack evolution in asphalt mixtures. Two types of graded asphalt mixtures (continuous gradation/AC and intermittent gradation/SMA) were scanned in-situ to capture internal structural changes. Digital image processing distinguished primary voids from cracks and extracted crack evolution. Multivariate regression analysis linked crack parameters to compressive strain. The study found that crack evolution during uniaxial compression in asphalt mixtures can be divided into densification, linear elastic deformation, and nonlinear failure stages. As load increases, the number, volume, and void percentage occupied by cracks rise, peak, and then decrease due to merging and engulfing after the ultimate load. The skeletal structure of cracks was obtained, and a damage evolution equation was established, linking crack parameters to damage evolution. Crack tortuosity was used to characterize the resistance effect of different gradations on crack propagation. This methodology provides new insights and technical support for studying damage evolution and understanding the failure mechanisms of asphalt mixtures. • Use in-situ CT technology to scan the uniaxial compression process of asphalt mixture. • Combine digital image processing technology and three-dimensional shape coefficients to distinguish internal voids and cracks in the specimen. • Quantitatively describe the evolution process of cracks under loading. • Establish a damage evolution equation between the damage variable and the vertical strain. [ABSTRACT FROM AUTHOR]

Current design methods rely mainly on the volumetric properties of asphalt mixtures. More comprehensive mixture analyses facilitate a broader understanding of the pavement performance as a function of factors such as traffic, climate, and mixture properties. Recently, performance-based mix designs have been developed to overcome shortcomings of the volumetric-based designs. Nevertheless, these new approaches may be time-consuming and expensive, and establishing a comprehensive understanding of the interplay between binder characteristics, volumetric properties, and performance outcomes becomes crucial. This work aims to explore relationships among these three aspects of asphalt mixtures regarding fatigue cracking and rutting performance. A database from different Brazilian studies and tests were collected. Data exploration analysis was conducted to evaluate the effect of the binder and volumetric properties on the fatigue and rutting results. The statistical analyses conducted in this study highlight that most properties within the database significantly impact asphalt mixture performance. Additionally, clear relationships were identified between various performance parameters. Lastly, multivariate analyses pinpointed key volumetric and binder variables that predominantly influence the mixture performance, particularly in relation to fatigue and rutting results. • Aggregate gradation and NMAS correlate with mixture volumetrics. • Moderate correlation exists between stiffness and fatigue parameters. • Binder properties are significantly correlated with mixture stiffness. • A Principal Component Analysis identified the binder primary role on mixture performance. • Volumetric properties play a substantial, but secondary role on mixture performance. [ABSTRACT FROM AUTHOR]

The increased Thermal Conductivity and Thermal Diffusion Coefficient of asphalt mixtures means that the material is able to conduct and disperse heat more efficiently. In winter, this property can be used to accelerate the melting process of snow and ice, reducing the risk of road sliding due to snow and ice build-up. In this study, the thermal conductivity, thermal diffusion coefficient, and specific heat capacity of phase change asphalt (PCA) mixtures were investigated using a transient flat-plate heat source method. Analysis was performed with a thermal constant analyzer, a custom-designed thermal conductivity experiment, and a differential scanning calorimeter. Additionally, a phase change asphalt mixture thermoregulation rutting plate was prepared to evaluate its thermoregulation and snow and ice resistance under actual winter and indoor conditions. Results indicated that the thermal conductivity and thermal diffusion coefficient of PCA mixtures were superior to those of conventional asphalt mixtures. Notably, the specific heat capacity of these mixtures increased significantly within the phase change temperature range. The integration of phase change materials enhanced heat transfer within the asphalt mixtures, allowing for a delayed cooling process when temperatures decreased, with the maximum cooling range observed to be 2.8°C. Snow melting tests confirmed the early snowfall efficacy of the phase change asphalt mixture rutting plate, effectively achieving minimal snow accumulation and demonstrating the capability of 'melting light snow.' • Development of a thermal diffusion coefficient testing method for phase change asphalt mixtures. • PCA mixtures have higher thermal conductivity and thermal diffusion coefficient. • The specific heat capacity of the PCA mixture exhibits a pronounced increase. • PCA mixtures significantly reduce cooling rates and extend cooling time by up to 42.5 minutes. • Incorporation of phase change materials into asphalt facilitates efficient early-stage snow melting. [ABSTRACT FROM AUTHOR]

In this research, machine learning (ML) based frameworks are developed to predict the in-plane mixed-mode fracture load of asphalt mixtures. In an initial stage, the RReliefF technique guides the selection of four parameters out of eight, namely fracture toughness, T-stress term, and modes I and II stress intensity factors (SIFs), to serve as inputs for predictive models. Subsequently, three ML models, namely support vector machine regressor (SVR), extra tree regressor (ETR), and gradient boosting regressor (GBR), are trained and tested using 675 experimental data points. Optimal hyper-parameter values for each model are determined through the particle swarm optimization (PSO) technique. To leverage the strengths of each individual model, two techniques, ensemble voting and stacking, are employed to combine the individual models. The performance of the presented models is assessed using 88 previously unseen datasets. The results underscore the significant promise of ML approaches for predicting the fracture load of asphalt mixture components, achieving accuracies of 90.48%, 91.11%, and 90.38% for SVR, ETR, and GBR, respectively. Notably, ensemble voting and stacking techniques further enhance predictive accuracy, achieving impressive accuracies of 91.25% and 91.57% respectively. Ultimately, model interpretation is accomplished via individual conditional expectation (ICE) plots, and the correlation of each predictor with the output is determined, which closely aligned with previous research findings and experimental observations. Our findings underscore the substantial potential of ML approaches in studying the fracture behavior of asphalt mixture components, with implications for enhancing infrastructure durability and safety. Compared to traditional analytical methods, ML-based frameworks offer improved accuracy and robustness in modeling the complex behavior of asphalt mixtures under varying conditions, thereby facilitating more precise assessments of infrastructure performance and durability. • Three ML models were built to predict the fracture load of asphalt mixtures. • Models were trained using 675 empirical data and assessed using 88 unseen data. • Using PSO enabled accurate choice of optimal hyper-parameters for each ML model. • Using RReliefF, fracture toughness emerged as the key feature for failure load. • ML models were interpreted to identify the correlation between predictors and target. [ABSTRACT FROM AUTHOR]

• A mechanistic model for quantitative analysis and prediction of the fatigue crack growth rate of paving materials is proposed. • The derived J-integral serves as the driving force for crack growth and it is a function of the horizontal tensile stress, initial resilient modulus, damage density, specimen size, and surface energy of the paving materials. • The fatigue life of cement-treated aggregates is primarily influenced by the crack initiation stage, while for asphalt mixtures, the crack growth stage plays a more significant role. • The Paris' law coefficients exhibit minimal variation across different stress levels and loading frequencies, and can be utilized to evaluate the fatigue crack resistance of paving materials. Fatigue crack growth rate (FCGR) is a critical indicator that reflects the rate at which material deterioration occurs under cyclic loads. However, there is currently a lack of a mechanistic quantitative analysis and prediction of the FCGR of paving materials under external indirect tensile (IDT) cyclic loads. To address this issue, this study aims to develop a mechanistic model for quantitative analysis and prediction of the FCGR in paving materials subjected to external IDT cyclic loads based on the J-integral based Paris' law. Two types of paving materials, namely cement-treated aggregates and asphalt mixtures, were selected to demonstrate the results and model of the FCGR. The results indicate that the derived J-integral serves as the driving force for crack growth and is influenced by horizontal tensile stress, initial resilient modulus, damage density, specimen size, and surface energy of the paving materials. The fatigue life of cement-treated aggregates is primarily influenced by the crack initiation stage, while for asphalt mixtures, the crack growth stage plays a more significant role. The application of Paris' law is found to be effective in predicting the FCGR at stable crack growth stage. The coefficients of Paris' law exhibit minimal variation across different stress levels and loading frequencies, and can be utilized to evaluate the fatigue crack resistance of different paving materials. [ABSTRACT FROM AUTHOR]

The compaction of asphalt mixture is crucial to the performance of the pavement. However, the mix design (i.e., porosity, aggregate size distribution, binder content), which is based on compaction results, remains largely empirical. It is difficult to relate the aggregate size distribution and the asphalt binder properties to the compaction curve in both the field and laboratory compaction of asphalt mixtures. In this paper, the author proposes a simple mathematical model from the perspective of granular physics to predict the compaction of asphalt mixtures. In this model, the compaction process is divided into two mechanisms: (i) viscoplastic deformation of an ordered granular-fluid assembly, and (ii) the transition from an ordered system to a disordered system due to particle rearrangement. This model could take into account both the viscous properties of the asphalt binder and the grain size distributions of the aggregates, where the viscous deformation is calculated with a proposed governing equation and the particle rearrangement effect is solved using simple DEM simulations. This model is calibrated based on the Superpave gyratory compaction tests in the pavement lab, and the R-squares of model predictions are all above 0.95. The model results are compared with experimental data to show that it can provide good predictions for the experiments, suggesting its potential for enhancing the design of asphalt mixtures.

In this study, the effect of seven industrial waste materials as mineral fillers in asphalt mixtures was investigated. Silica fume (SF), limestone dust (LSD), stone dust (SD), rice husk ash (RHA), fly ash (FA), brick dust (BD), and marble dust (MD) were used to prepare the asphalt mixtures. The obtained experimental results were compared with ordinary Portland cement (OPC), which is used as a conventional mineral filler. The physical, chemical, and morphological assessment of the fillers was performed to evaluate the suitability of industrial waste to replace the OPC. The volumetric, strength, and durability of the modified asphalt mixes were examined to evaluate their performance. The experimental data have been processed through artificial neural networks (ANNs), using k-fold cross-validation as a resampling method and two different activation functions to develop predictive models of the main mechanical and volumetric parameters. In the current research, the two most relevant parameters investigated are the filler type and the filler content, given that they both greatly affect the asphalt concrete mechanical performance. The asphalt mixes have been optimized by means of the Marshall stability analysis, and after that, for each different filler, the optimum asphalt mixtures were investigated by carrying out Indirect tensile strength, moisture susceptibility, and abrasion loss tests. The moisture sensitivity of the modified asphalt mixtures is within the acceptable limit according to the Indian standard. Asphalt mixes modified with the finest mineral fillers exhibited superior stiffness and cracking resistance. Experimental results show higher moisture resistance in calcium-dominant mineral filler-modified asphalt mixtures. Except for mixes prepared with RHA and MD (4% filler content), all the asphalt mixtures considered in this study show MS values higher than 10 kN, as prescribed by Indian regulations. All the values of the void ratio for each asphalt mix have been observed to range between 3–5%, and MQ results were observed between 2 kN/mm–6 kN/mm, which falls within the acceptable range of the Indian specification. Partly due to implementing a data-augmentation strategy based on interpolation, the ANN modeling was very successful, showing a coefficient of correlation averaged over all output variables equal to 0.9967. [ABSTRACT FROM AUTHOR]

The permanent deformation of asphalt pavement under similar traffic conditions depends on a number of factors. The factors considered in this study are bitumen source, aggregate source, aggregate gradation, bulk specific gravity of aggregates (Gsb), percentage of aggregates passing #4 sieve, air voids (Va), optimum bitumen content, binder grade, load repetitions, temperature, and Marshall stability. Asphalt pavement analyzer (APA) test, Cooper wheel tracking test (CWTT), and repeated load axial test (RLAT) were performed on thirteen different types of hot mixed asphalt (HMA) mixtures. Three artificial neural network (ANN) algorithms, namely Backpropagation (BP), Conjugate gradient (CG), and Broyden-Fletcher Goldfarb-Shanno (BFGS) were used to analyse the data. The best fit ANN algorithm for each of the laboratory tests (APA, CWTT, RLAT) was selected, based on the coefficient of determination (R-squared), root-mean-square error (RMSE), mean bias error (MBE) and the mean square error (MSE) closest to the gamma statistic Г. The results showed no single ANN algorithm is suitable for predicting all HMA rutting susceptibility tests data. The BP algorithm most appropriately predicts APA test data, the BFGS algorithm precisely fits CWTT results, and the CG algorithm seems most suitable to predict RLAT data. However, further, differentiating testing is required for a more precise comparison of rutting predicting ability of various ANN algorithms. [ABSTRACT FROM AUTHOR]

In the past, most researchers have explained the three-stage creep behavior of asphalt mixture in detail. Still, there is no reasonable model to describe the creep of the consolidation effect. To accurately describe the consolidation effect of an asphalt mixture during the viscoelastic deformation process, a modified time hardening model was established by using the Malthus model and the Logistic function to change its creep strain and creep compliance. According to the characteristics of asphalt mixture creep, a single penetration creep test was conducted for high-elasticity modified asphalt mixtures at different temperatures (20 °C, 40 °C, 60 °C) and various loading levels (0.55 MPa, 0.70 MPa, 0.85 MPa, 1.00 MPa). The test results showed that the effect of stress on deformation within the normal range of variation was more significant than that of temperature. In addition, the test results were simulated by the modified time hardening model using surface fitting and compared with a time hardening model and a modified Burgers model. A fitting analysis showed that the modified time hardening model more accurately represents the asphalt mixture's consolidation effect and creep behavior. Therefore, the modified time hardening model can better show the consolidation effect in the creep process. [ABSTRACT FROM AUTHOR]

Asphalt mixtures, composed of air, aggregate (limestone), and asphalt (matrix), are sensitive to temperature. In order to clarify the influence of temperature on the dielectric properties of asphalt mixtures and improve the accuracy of ground-penetrating radar (GPR) testing, this paper investigates the dielectric properties of limestone, two types of asphalt [Asphalt 70 and styrene-butadiene-styrene (SBS)–modified asphalt] and asphalt mixtures [stone matrix asphalt (SMA) and SBS-SMA mixtures] covering temperature range of −30°C to 60°C using the open-ended coaxial probe kit method and waveguide cavity method, respectively. The results indicate that the dielectric constants and loss factors of limestone, asphalt, and asphalt mixtures increase in various degrees with the increase of temperature. Approximately linear relationships between the dielectric constants and loss factors of limestone, asphalt, and asphalt mixtures and temperature are discerned. This denotes the influence of temperature on the dielectric properties of asphalt mixtures is not negligible. At the same time, the accuracy of nondestructive testing and evaluation of asphalt pavement based on GPR technology highly depends on the composite dielectric model of asphalt mixtures. Via the introduction of temperature coefficients, the dielectric regression model of asphalt mixtures considering the effect of temperature is established. Compared with the traditional dielectric models, the proposed model has higher accuracy. [ABSTRACT FROM AUTHOR]

This research recommends a mathematical modelling approach to determine flow time (FT). The scope of the work includes the collection and analysis of the static creep test data for asphalt mixtures produced using two different nominal maximum aggregate size (NMAS) values and two base binder grades. Modifiers of styrene butadiene styrene (SBS), polyphosphoric acid (PPA) and combination of them are selected to consider a wide range of testing times from 120 to 30,000 s. The FTs of the mixtures are determined using three techniques: the method developed in national cooperative highway research programme (NCHRP) Report 465, the Francken model, and the proposed mathematical model which is based on the ordinary tangent function. The results show that the NCHRP method is sensitive to the user-selected size of logarithmic scale unit of time, causing difficulties in the FT computation. It is also shown that the Francken model, often used to fit the dynamic creep curves, cannot completely fit the static creep test data, and so is not capable of estimating FT, properly. However, based on the limited data available in this study, the proposed tangent model performs very well in characterising all the three stages of the static creep curve and estimates the accurate value of FT in a reasonable time. Because of the simplicity, computational speed and accuracy of the proposed tangent model, it can be considered as an alternative to the NCHRP method to determine FT. [ABSTRACT FROM AUTHOR]

Skid resistance is a key factor in road safety. Surface friction characteristics of roads are dependent on the microtexture and macrotexture of the surface. The decay of skid resistance with time is a function of traffic level and aggregate characteristics. This study developed predictive models for skid resistance of asphalt pavements and seal coat surfaces. The researchers examined the surface friction characteristics of 35 asphalt pavement test sections and 35 seal coat test sections. The skid number was measured using a skid trailer, while the microtexture and macrotexture of the test sections were measured using a dynamic friction tester and a circular texture meter, respectively. The Aggregate Image Measurement System (AIMS) and Micro-Deval test were also used to evaluate the aggregate shape properties and its resistance to polishing and abrasion. The developed skid prediction models express the skid number over time as a function of aggregate gradation, aggregate resistance to abrasion and polishing, and traffic level. The models showed good correlations with skid numbers measured in the field. These models can be used to optimise the mix design to provide adequate level of friction and estimate the skid number of asphalt pavements and seal coat surfaces over time. [ABSTRACT FROM AUTHOR]

Asphalt mixtures are commonly used in pavement engineering, especially for highway construction. The mechanism exploration and analysis of pavement distress are the main challenges for researchers and industry managers. Thereby, it is important to understand their properties and interaction mechanisms in asphalt mixtures. It is difficult to conduct some sophisticated or microscale tests in the laboratory, and numerical simulation and virtual tests can be solutions for these cases with low costs. The Discrete Element Method (DEM) is a promising tool for researchers to undertake these tasks. This paper mainly summarized and analyzed the research progress and development prospect of DEMs in asphalt mixtures from a series of technical sections. The laboratory test results were often used to calibrate the DEM simulations as well as Two-dimensional (2D) and Three-dimensional (3D) modeling. Several modeling methods were developed to generate digital samples, like user-defined, image-based, random-modeling. In addition, the conclusions can be referenced by researchers for the development of numerical simulations.

Asphalt aging is recognised as one of the important factors causing cracking related failures in asphalt pavements. Asphalt aging occurs during production, construction, and service life of the asphalt surfaced pavements. Since constituents of asphalt mixtures are continuously increasing (increased recycled asphalt pavement (RAP), rejuvenators, compaction aids, warm-mix additives, fibres, etc.) and interactions between these constituents are complicating the mixture design process, relying solely on the volumetric mixture design is usually not resulting in asphalt mixtures with the highest possible performance. Thus, asphalt mixture test methods for rutting and cracking should be improved and incorporated into current mixture design methods to be able to develop more durable asphalt mixtures that last for their intended service lives. In this study, the most effective asphalt mixture long-term aging protocol was determined to achieve reliable semi-circular bend (SCB) test parameters that are correlated with in-situ cracking performance. The selected aging protocol will be integrated into the balanced mix design procedures that are currently being developed. Developed asphalt mixture design methods are expected to improve the longevity of asphalt materials, reduce life-cycle costs for agencies, and improve long-term road users' comfort. [ABSTRACT FROM AUTHOR]

Owing to the existence of high hydrodynamic pressure in heavy traffic conditions, moisture will diffuse quickly into the asphalt mixtures, which will induce the adhesive failure of asphalt mixtures and shorten the service life of asphalt pavement. This research aims at solving the problems of moisture diffusion and distribution of asphalt mixtures, especially in heavy traffic conditions. The moisture diffusion paths, moisture distribution and the susceptible areas of moisture damage were investigated by molecular dynamics simulations, numerical simulation and experiments. The slope of fatigue lifetime function of OGFC-13 (1.0 atm), OGFC-13 (1.5 atm) and OGFC-13 (2.0 atm) is −4.23, −4.22 and −4.20, respectively. It shows that hydrodynamic pressure affects the fatigue lifetime and reduces the durability of asphalt mixtures. The moisture diffusion path is three-dimensional tortuous curves, and moisture distribution is related to air voids or mixtures types of asphalt mixtures, and the moisture diffusion coefficient of z-direction is the biggest in heavy traffic condition. Moreover, the length of moisture diffusion paths is more than the thicknesses of the asphalt mixtures. [ABSTRACT FROM AUTHOR]

Copper slag is considered a mining environmental liability and is usually deposited in landfills. However, some investigations have been oriented to their use in mortars and concretes. On the other hand, no studies have been reported on the use of copper slag from abandoned landfills of the 19th century in the design of asphalt pavements. In this study, the behaviour of hot asphalt mixtures containing copper slag from abandoned landfill in northern Chile, as a partial substitute for coarse aggregate was evaluated. For the design and control of bituminous pavement mixtures, the Marshall method was used. The parameters evaluated were density, % air voids in the mixture, % voids in the mineral aggregate, creep and stability. In addition, asphalt mixtures containing 4.5 to 6.0% were evaluated with increments of 0.5% asphalt for four types of mixtures with partial substitution of conventional aggregates by copper slag (0, 30, 50 and 70%, by weight). In conclusion, it can be pointed out that the mixture with 5% asphalt and 30% copper slag in replacement of the aggregate is the most suitable mixture and could be used in the design of asphalt mixtures for pavements. The use of copper slag from abandoned landfills in the manufacture of asphalt pavements, would contribute to improving environmental conditions, also decreasing the demand for aggregates in desert areas such as the Atacama Region in Chile. [ABSTRACT FROM AUTHOR]

The main objective of this research is to investigate the rutting of modified mixtures with two additives of crumb rubber and polyethylene terephthalate (PET).Therefore, ITS method, resilient modulus and Dynamic creep were used to investigate asphalt behaviour with these two additives in this article. Modified blends include ten blends that are made by combining crumb rubber and polyethylene terephthalate in various percentages. The modifiers are combined in two percent 10% and 15% with 60/70 penetration bitumen. Finally, with these mentioned tests, the results of the ten modified samples along with the non-modified one were compared. The results showed that the addition of polyethylene terephthalate increased the viscosity and reduced the density; therefore, addition of more polyethylene terephthalate in the modifier reduces the flow number and, on the other hand, addition of 15% modifier containing polyethylene terephthalate resilient module increases the flow number by about 66%. Ultimately, neural network method was used to predict the result of dynamic creep test; indirect tensile strength and the capability of neural network method have been measured to estimate the laboratory result. According to the results, ANFIS can estimate the laboratory data correctly.

There are various experimental methods for improving the moisture strength of asphalt concrete, such that the most common one being the use of anti-stripping materials. In the present paper, the influences of polymer materials on\ asphalt binder were investigated using repetitive loading test in wet and dry conditions along with thermodynamic parameters based on the surface free energy (SFE) components of asphalt binder and aggregates. The obtained results of this investigation indicate that using styrene butadiene rubber (SBR) polymer has improved the asphalt concrete strength against the moisture damage, especially in the specimens made of granite aggregates. Also, SBR polymer increases the cohesion free energy and reduces the energy released by the system during the stripping event, which represents a decrease in the tendency for stripping. The stripping percentage index, which is obtained by combining the results of the repetitive loading test in wet and dry conditions along with the results of thermodynamic parameters, represents that the specimens made of controlled asphalt binder in the loading cycles under wet conditions have a higher stripping rate. Also, the modulus loss rate in control asphalt concrete is faster than the modified specimens.

Asphalt crumb rubber is a type of pavement material formed by mixing asphalt cement with crumb rubber that is derived from recycled tires. This eco-friendly approach aids in waste reduction and promotes environmental preservation by incorporating recycled materials into pavement construction. The study aimed to examine the behavior of asphalt mixtures modified with crumb rubber, made by blending recycled tire-derived crumb rubber with asphalt cement. Adding crumb rubber improved the performance of asphalt mixtures, with 8% crumb rubber enhancing the Marshall stability by 20% and 34% for 40/50 and 50/60 grades, respectively. The moisture susceptibility of both grades also improved. Crumb rubber is a sustainable material that can improve the performance of asphalt mixtures.

Reclaimed asphalt pavement (RAP) is considered one of the valuable alternatives to raw materials due to reducing the need to use raw materials, which are less in some world regions. It additionally reduces the highly-priced new bitumen required inside the asphaltic mixture manufacturing and contributes to the preservation of natural resources. To achieve maximum benefit from the integration RAP in asphaltic mixture, it is necessary to investigate the advantages and disadvantages of the recycling process on the properties of asphalt pavement. This study examines the effect of adding reclaimed asphalt pavement by different percentages on the mechanical properties of asphaltic mixture for the surface layer in terms of Marshall's stability, Retained Marshall stability, indirect tensile strength, and compressive strength. Two types of asphalt grade (40-50) and (60-70) were used in addition to one type of aggregate gradation of the wearing course to prepare the asphaltic mixture. The Superpave system was applied to select the best aggregate gradation and optimum asphalt content using Superpave Gyratory Compactor (SGC) and to prepare compacted asphaltic specimens of 100 mm diameter for simulating Marshall’s molds. PAP is added by four different percentages of (7, 13, 19, and 25) % by the weight of the total asphalt mixture, and samples are prepared to compare the mechanical properties with conditional ones. The results show that adding RAP to the asphalt mixture improved the measured properties. In contrast, the mix containing RAP showed lower loss of stability, lower loss in indirect tensile strength, higher stripping resistance, and better durability than the mixture without RAP.

Adding basalt fiber (BF) can effectively enhance the performance of asphalt mixtures and improve the service quality of asphalt pavement. However, the effect of BF on the high-temperature performance of different types of asphalt mixtures and systematic high-temperature performance test analysis are still not well known. To address this issue, three typical types of asphalt mixtures of AC-13, SMA-13, and SUP-13 were selected. Wheel tracking test, uniaxial penetration test, dynamic modulus test, and dynamic creep test were conducted. In addition, relevant parameters of dynamic stability, penetration strength, dynamic modulus index, and flow number were analyzed. The results showed that adding BF into the asphalt mixture could improve the dynamic stability, penetration strength, dynamic modulus index, and flow number significantly, indicating that adding basalt fiber is an effective solution to the rutting deformation damage of asphalt pavement. Moreover, the parameter of dynamic stability presented an approximate polynomial correlation with penetration strength, dynamic modulus index, and flow number, respectively. These findings provide a certain theoretical reference for evaluating the high-temperature performance of BF-modified asphalt mixtures.

In recent years, the attention of many researchers in the field of pavement engineering has focused on the search for alternative fillers that could replace Portland cement and traditional limestone in the production of asphalt mixtures. In addition, from a Czech perspective, there was the need to determine the quality of asphalt mixtures prepared with selected fillers provided by different local quarries and suppliers. This paper discusses an experimental investigation and a machine learning modeling carried out by a decision tree CatBoost approach, based on experimentally determined volumetric and mechanical properties of fine-grained asphalt concretes prepared with selected quarry fillers used as an alternative to traditional limestone and Portland cement. Air voids content and stiffness modulus at 15 °C were predicted on the basis of seven input variables, including bulk density, a categorical variable distinguishing the aggregates’ quarry of origin, and five main filler-oxide contents determined by means of X-ray fluorescence spectrometry. All mixtures were prepared by fixing the filler content at 10% by mass, with a bitumen content of 6% (PG 160/220), and with roughly the same grading curve. Model predictive performance was evaluated in terms of six different evaluation metrics with Pearson correlation and coefficient of determination always higher than 0.96 and 0.92, respectively. Based on the results obtained, this study could represent a forward feasibility study on the mathematical prediction of the asphalt mixtures’ mechanical behavior on the basis of its filler mineralogical composition.

In recent years, due to the reduction in available natural resources, the attention of many researchers has been focused on the reuse of recycled materials and industrial waste in common engineering applications. This paper discusses the feasibility of using seven different materials as alternative fillers instead of ordinary Portland cement (OPC) in road pavement base layers: namely rice husk ash (RHA), brick dust (BD), marble dust (MD), stone dust (SD), fly ash (FA), limestone dust (LD), and silica fume (SF). To exclusively evaluate the effect that selected fillers had on the mechanical performance of asphalt mixtures, we carried out Marshall, indirect tensile strength, moisture susceptibility, and Cantabro abrasion loss tests on specimens in which only the filler type and its percentage varied while keeping constant all the remaining design parameters. Experimental findings showed that all mixtures, except those prepared with 4% RHA or MD, met the requirements of Indian standards with respect to air voids, Marshall stability and quotient. LD and SF mixtures provided slightly better mechanical strength and durability than OPC ones, proving they can be successfully recycled as filler in asphalt mixtures. Furthermore, a Machine Learning methodology based on laboratory results was developed. A decision tree Categorical Boosting approach allowed the main mechanical properties of the investigated mixtures to be predicted on the basis of the main compositional variables, with a mean Pearson correlation and a mean coefficient of determination equal to 0.9724 and 0.9374, respectively.

Asphalt rubber mixtures have been used as pavement surface layers due to their ability to prevent early degradation, and are considered a sustainable option. This study performed analysis comparing the fatigue resistance of asphalt rubber mixtures of different combinations of asphalt bases, crumb rubber, and gradation, in order to estimate the performance of asphalt rubber mixtures as pavement surface layers. The methodology was developed in a laboratory and involved asphalt rubber production by continuous and terminal blend systems with different crumb rubbers and asphalt base types. Asphalt rubber mixtures with varying gradations and an unmodified asphalt mixture as a reference were produced. The mechanical behavior as a dynamic modulus and with respect to fatigue resistance was evaluated using a four-point bending test. In order to verify each of the asphalt rubber mixtures’ contribution as a surface layer, pavement structures were designed and their lifespans were compared. The findings showed that all asphalt rubber mixtures presented higher fatigue resistance than the reference. For pavement design, in comparison with the reference mixture, the thickness of the surface layer could be reduced by at least 50% while achieving the same life, proving its successful performance. This study demonstrated the effective contribution of crumb rubber from scrap tires as an asphalt modifier for producing sustainable mixtures with adequate fatigue performance.